The present invention relates to an improved filter device for filtering, entrapping air, and preventing foaming in fluids, such as biological matter, including whole blood or blood components. More specifically, the invention relates to a filter assembly having an injection molded filter housing and a method of making a filter housing for performing the same. The invention may be used in blood collection and processing systems for removing leukocytes from whole blood, red blood cells, plasma, and platelets prior to transfusion or long term storage.
It is common in the formation of medical and laboratory filters, such as blood filters or blood filtration housings containing filters, to form filter housings for filter media from one or more sheets of flexible polyvinyl chloride (PVC) material. It is also common to manufacture filter housings from rigid plastics such as acrylic, polypropylene, or a similar material.
Many types of devices are commercially available for separating whole blood components. Some machines are fully automated while others rely on manual operations performed by technicians. On a gross level, blood components include plasma (water and protein), red blood cells, leukocytes, and platelets. Filter media is commercially available to filter leukocytes from blood. A filter pad media for filtering leukocytes from blood cells is disclosed in U.S. Pat. No. 5,591,337, commonly owned by the assignee hereof.
While filter housings manufactured from flexible PVC material offer the benefit of having a flexible housing, it has been heretofore difficult to provide an efficient and reliable method for forming an inlet port and an outlet port in the filter housing. Prior art filter housings made from one or more sheets of PVC material have taught the formation of the port along the peripheral seal of the respective PVC material sheet edges. Typically, a short piece of tubing is used as the port. See, for example, U.S. Pat. No. 4,035,304 to Watanabe issued Jul. 12, 1977 and entitled Blood Filtering Bag. However, it is difficult to form a complete and reliable seal at the junction of the PVC material sheets and the tubing that serves as the port. Both an incomplete seal, as well as a weak seal can lead to fluid leaking from the filter assembly during the filtering process.
Introducing fluid into a filter housing at the seal of its panels or sheets is also less desirable when the flow characteristics of the fluid across the filter media are important (e.g. laminar flow or even flow across the filter media). If the fluid enters the housing immediately adjacent the filter media, the bubble strength of the filter media may be quickly surpassed by increased blockage of the filter media with filtered particulate and the resulting increased pressure within the filter housing may cause the filter media to rupture or burst. This is a very undesirable result in that it is difficult, if not impossible to immediately detect a ruptured filter membrane. Alternatively, increased blockage of the filter media may lead to turbulent fluid flow through the filter assembly. Many fluids react poorly to turbulent flow.
A similar prior art filter is taught in published European Patent Publication No. 0 516 846 to Sakamoto published Dec. 9, 1992 and entitled Bag-Like Filter. This application teaches the formation of filter housings from heat-fusible polyethylene films. In one embodiment the inlet and outlet ports are formed from polyethylene tubing fused between the film and the filter at their edges. Alternatively, separate inlet and outlet ports having a construction similar to a valve placed in a tire tube may be fused through an opening formed in the central regions of the film sheets.
Other prior art devices, such as U.S. Pat. No. 5,507,904, commonly owned by the assignee hereof, teach the formation of the inlet and outlet ports in the wall of a thermoplastic sheet filter housing by first forming a slit in the filter housing wall, inserting a separate tube through the slit and heating the mating materials to fuse the tube and sheet. While providing a very reliable filter assembly, extra care must be taken during the manufacturing process to ensure that the slit is not too large, the tube is properly placed prior to heating, and a good seal is formed around the tubing-wall junction. Some prior art filter assemblies do not include positive stops for the conduits attached to their filter ports. Without a stop, the possibility exists that the rubber or plastic conduit may be inserted too far into the port, thereby possibly damaging or piercing the filter media. In addition, if solvent is used to bond the conduit to the port, the solvent may contact and thereby degrade the filter media.
Filter housings molded from hard plastics such as acrylic allow for the formation of the inlet and outlet ports at almost any location along the wall or panel of the filter housing. The location is primarily limited only by the sophistication of the mold or die. However, the resulting filter assemblies have the drawback that they are not flexible and thus cannot substantially prevent a phenomenon common in fluid filtering processes known as xe2x80x9cfoaming.xe2x80x9d It is also sometimes necessary to centrifuge a blood container having a filter device attached thereto. A hard plastic filter housing may puncture or damage the blood container during the centrifuge process.
Most of the whole blood collected from donors today is not itself stored and used for transfusion. Instead, the whole blood is separated into its clinically proven components (typically red blood cells, platelets, and plasma), which are themselves individually stored and used to treat a multiplicity of specific conditions and diseased states. For example, the red blood cell component is used to treat anemia; the concentrated platelet component is used to control thrombocytopenic bleeding; and the platelet-poor plasma component is used as a volume expander or as a source of Clotting Factor VIII for the treatment of hemophilia.
Automated centrifugal blood collection systems and manual systems composed of multiple, interconnected plastic bags have met widespread use and acceptance in the collection, processing and storage of these blood components. In the United States, these systems are subject to regulation by the government. For example, the plastic materials from which the bags and tubing are made must be approved by the government. In addition, the maximum storage periods for the blood components collected in these systems are prescribed by regulation.
In the United States, whole blood components collected in a non-sterile, or xe2x80x9copenxe2x80x9d, system (e.g. one that is open to communication with the atmosphere) must, under governmental regulations, be transfused within twenty-four hours. However, when whole blood components are collected in a sterile, or xe2x80x9cclosedxe2x80x9d, system (e.g., one that is closed to communication with the atmosphere), the red blood cells can be stored up to forty-two days (depending upon the type of anticoagulant and storage medium used); the platelet concentrate can be stored up to five days (depending upon the type of storage container); and the platelet-poor plasma may be frozen and stored for even longer periods. Conventional systems of multiple, interconnected plastic bags have met with widespread acceptance, because these systems can reliably provide the desired sterile, xe2x80x9cclosedxe2x80x9d environment for blood collection and processing, thereby assuring the maximum available storage periods.
In collecting whole blood components for transfusion, it is desirable to minimize the presence of impurities or other materials that may cause undesired side effects in the recipient. For example, because of possible febrile reactions, it is generally considered desirable to transfuse red blood cells substantially free of the white blood cell components, particularly for recipients who undergo frequent transfusions.
One way to remove leukocytes is by washing the red blood cells with saline. This technique is time consuming and inefficient, as it can reduce the number of red blood cells available for transfusion. The washing process also exposes the red blood cells to communication with the atmosphere, and thereby constitutes a xe2x80x9cnon-sterilexe2x80x9d entry into the storage system. Once a non-sterile entry is made in a previously closed system, the system is considered xe2x80x9copenedxe2x80x9d, and transfusion must occur within twenty-four hours, regardless of the manner in which the blood was collected and processed in the first place. In the United States, an entry into a blood collection system that presents the probability of non-sterility that exceeds one in a million is generally considered to constitute a xe2x80x9cnon-sterilexe2x80x9d entry.
Another way to remove leukocytes is by filtration. Systems and methods for accomplishing this within the context of conventional multiple blood bag configurations are described in Wisdom U.S. Pat. Nos. 4,596,657 and 4,767,541, as well as in Carmen et al U.S. Pat. Nos. 4,810,378 and 4,855,063. In these arrangements, an inline leukocyte filtration device is used. The filtration can thereby be accomplished in a closed system. However, the filtration processes associated with these arrangements require the extra step of wetting the filtration device before use with a red blood cell additive solution or the like. This added step complicates the filtration process and increases the processing time.
Other systems and methods for removing leukocytes in the context of closed, multiple blood bag configurations are described in Stewart U.S. Pat. No. 4,997,577. In these filtration systems and methods, a transfer assembly dedicated solely to the removal of leukocytes is used. The transfer assembly is attached to a primary blood collection container. The transfer assembly has a transfer container and a first fluid path leading to the transfer container that includes an inline device for separating leukocytes from red blood cells. The transfer assembly also has a second fluid path that bypasses the separation device. Using these systems and methods, leukocytes are removed as the red blood cells are conveyed to the transfer container through the first fluid path. The red blood cells, now substantially free of leukocytes, are then conveyed from the transfer container back to the primary collection container for storage through the second fluid path, this time bypassing the separation device.
A need still exists for an improved biological matter filter housing that is flexible and that includes an inlet or an outlet port integrally formed in the housing. A need exists for an improved filter housing capable of trapping air and preventing foaming of the fluid or blood passed through the filter. A need also exists for a form of a fluid filter having an inlet and an outlet formed tangentially in a flexible wall of the filter assembly. A need exits for an improved flexible filter housing having integral ports including positive stops for conduits connected to the filter also exists. Because these types of devices are often used only once (e.g. disposable) a need exists for an efficient, reliable and low cost method of making the filter assembly.
It is a principle object of the present invention to provide an improved filter device having a body defined by at least one injection molded, flexible filter housing element sealed to form an interior chamber. A filter medium is located within the chamber. The housing element has at least one port integrally molded therein. The integrally formed ports are tangential or substantially tangential to the filter housing walls and parallel to the filter medium.
In one embodiment, a filter device is provided and defined by at least one injection molded housing element having a flexible portion formed therein and sealed along edges thereof to form an interior cavity. A filter membrane is sealed within the cavity. At least one port, in fluid communication with the interior cavity, is integrally molded in the flexible portion. In a specific application, the port is positioned tangentially with respect to the flexible portion and the filter device is positioned horizontally with respect to the port.
In another embodiment the filter device comprises first and second generally flexible injection molded filter housing elements, each element having a flange formed about a periphery thereof and a domed portion formed therein. At least one port is molded in the domed portion. The filter housing elements arranged along their respective flanges to form an interior cavity and a filter membrane, having an outer periphery, is positioned between the filter housing elements. The first filter housing element flange, the filter membrane outer periphery and said second filter housing element flange are sealed together to form an interior cavity. Each port is in fluid communication with the interior cavity.
In another embodiment, the invention includes a container comprising an injection molded sheet having a substantially flexible portion integrally molded therein. The sheet is sealed along an edge after injection molding forming an interior chamber and at least one port is integrally formed in the flexible portion of the sheet. The port is in fluid communication with the interior chamber.
In yet further embodiments, a blood processing system is disclosed including a first bags, a second bag, and tubing providing communication between the two bags and including a blood filter or device of a type described above.
For example, the invention may be utilized in a multiple container blood collection system for conveniently processing the various components of blood. In such a system, the filter device of the present invention performs the function of separating the undesired matter, e.g., leukocytes, during processing. The system is arranged so that some blood components can be conveyed through the filter device, while other components can be readily conveyed along other paths that bypass the filter device.
An important aspect of the invention is that the filter housing element or elements are flexible thus allowing the filter device to expand and contract during the filtration process. In a preferred embodiment, the filter housing elements are dome-like in structure and the inlet or outlet port is molded in a central region of the dome. Due to its flexible structure, the filter device is capable of minimizing foaming of the fluid passed therethrough. The volume of the interior chamber is capable of increasing and decreasing its volume during the filtration process. While the filter medium is initially spaced a predetermined distance from the housing element, this distance may also change during the filtration process.
Another important aspect of the invention is that the filter device is capable of trapping air while in a horizontal orientation. In this orientation, the inlet port is positioned on the upper surface of the device and the outlet port is positioned on the lower surface. Accordingly, the present invention is well suited for applications on horizontal planes (e.g. the top panel of an instrument).
Yet another important aspect of the invention is that each filter element is injection molded thus producing a unitary, single filter element including a flexible portion and an integrally molded fluid port. The fluid ports include a port opening extending from the exterior of the element, through its flexible portion and into the element interior. The filter device inlet and outlet ports may include structure for limiting the insertion of a conduit therein. In a preferred embodiment, the filter elements may be molded from a thermoplastic material, such as polyvinyl chloride.
The filter media or medium enclosed within the filter device may be any of a great number of known filtration materials. As one example, the filter medium may comprise a polyester mesh material. In a specific application of the filter device, the filtration material is may be selected to remove undesirable materials, such as leukocytes, from whole blood, red blood cells, platelet rich plasma, platelet poor plasma or platelet concentrate. Examples of these filtration materials can be found in the following patents: U.S. Pat. Nos. 5,591,337, 5,089,146, 4,767,541, 5,399,268, 5,100,564, 4,330,410, 4,701,267, 4,246,107, 4,936,998 and 4,985,153. Each of these patents is incorporated herein by reference.
In accordance with a related aspect, the possibility of damaging or piercing the filter medium is eliminated by the inclusion of structure within the port opening that forms a stop. This aspect is particularly important when it is desirable to connect a conduit to the filter assembly using only an interference fit between the conduit and the port opening.
The first and second filter housings may be identical to one another. In this manner, the orientation of the filter ports can be readily positioned during the manufacturing process in the same direction or in opposed directions, depending upon the fluid to be passed through the filter, the filter medium and/or the location and application constraints of the filter device.
In accordance with an important specific application of the invention, the filter device may be incorporated into an apparatus for collecting and separating the various components of whole blood, e.g. red blood cells, platelets and blood plasma. The apparatus may be an automated blood separation apparatus or manual apparatus.
In accordance with another aspect of the invention, an injection molding die is provided to mold from a thermoplastic material filter housing elements, each having a flange portion, a flexible central region and an integral port. A second pair of opposed dies is provided to seal filter media between first and second filter housing elements. The dies, which are formed of an electrically conductive material are positioned so that the first housing element, filter media, and a second housing element are placed between said dies. When RF energy is transmitted to the flange portions of the first and second filter housings through the conductive dies, the thermoplastic material is caused to soften or melt and to flow to seal the periphery of the filter media between the housing elements.
In a preferred method of forming the fluid filter device from a thermoplastic material, the method comprises the steps of injection molding first and second flexible filter housings, each housing having a port integrally formed therein and having a periphery thereabout; placing a filter membrane between said first and second filter housing peripheries; and sealing along the periphery of the filter housing to form a fluid tight enclosure. In addition, the resulting enclosure may be trimmed in a cutting die to produce a more aesthetically pleasing filter device.
The fusing or sealing step may be conducted by placing the metallic dies on opposite sides of the filter housings and applying energy to the peripheries to dielectrically heat said peripheries to cause softening and sealing thereof. Alternatively, the fusing or sealing step may be conducted by the application of radio frequency energy.
Multiple filter housing elements may be molded and multiple filter housing assemblies may be formed at the same time. Utilizing this method a third cutting die is provided to individually cut each completed filter assembly from a carrier web.
Further advantages and aspects of the invention will be apparent from the following detailed description and accompanying drawings.